Upgrading to Ruby on Rails 4.1 was much easier than moving from 3.2 to 4.0. Maybe because I try to keep all the apps up-2-date, maybe because Rails guys didn’t change much stuff ;) (or maybe both). Either way, lets get through it.

Paperclip – String based terminators are deprecated, please use a lambda

DEPRECATION WARNING: String based terminators are deprecated, please use a lambda.
(called from has_attached_file at app/config/initializers/paperclip_extensions.rb:22)

The ability to pass in strings as a class name to set_fixture_class
will be removed

Next deprecation warning:

DEPRECATION WARNING: The ability to pass in strings as a class name to `set_fixture_class`
will be removed in Rails 4.2. Use the class itself instead.
(called from block in initialize at gems/activerecord-4.1.0/lib/active_record/fixtures.rb:465)

It you use Rspec you probably won’t see this issue at all (or if you don’t use fixtures). One of my apps unfortunately still does. Solution to this is really simple. Instead of:

# This will throw an error
@articles = Article.limit(10).order('created_at DESC').reverse!

Instead you have to cast ActiveRecord::Relation to an array:

@articles = Article.limit(10).order('created_at DESC').to_a.reverse!

Keep in mind, that casting with to_a will deprive you from all benefits of lazy loading with Rails relations so use it carefully. But on the other hand, reverse! on ActiveRecord::Relation did the same, so if you used it and it was ok, than feel free ;)

Other issues

Well to be honest I didn’t have any more issues. I’ve decided to remove Squeel gem from all of my projects, since it is not currently maintained. Thanks to that I’ve finally got rid of this irritating deprecation warning:

DEPRECATION WARNING: Core extensions are deprecated and will be removed in Squeel 2.0.
(called from /app/config/initializers/squeel.rb:2:in `block in <top (required)>')

Summary

Rails 4.1 is not a big step, although it is a required one if you want to upgrade to 4.2 in the future. If you have decent test coverage level, you should not have big issues with this upgrade.